1. Field of the Invention
The present invention pertains to probes for obtaining soil samples below the surface of the ground.
2. Description of the Prior Art
It has long been desirable to obtain samples of subterranean soil conditions for various purposes. Early uses of soil samples were determination of soil conditions prior to construction of structures on the ground and attempted location of mineral deposits. Devices for obtaining such samples vary with the type of sample required.
A large number of contemporary uses for samples require only a relatively small sample, on the order of 25 cm (10") long with a 2.5 cm (1") diameter, taken from a particular depth which is often somewhat greater than 9 meters (30'). While still useful for determining construction site suitability, such samples are also used in studies of chemical dissipation and residue, determination of concentration of environmental contaminants, investigating of hazardous waste sites and other uses.
A known device for taking such samples is produced by the Acker Drill Co., Inc. of Scranton, Pa. This device consists of a cylindrical sample casing open at both ends. A rearward end of the casing is threaded to receive a similar cylindrical extension. Successive extensions are added, by threading, to extend the casing to the desired depth.
A plug is located in the casing at the forward end during driving of the casing to ensure that soil does not enter the casing until the proper depth is reached. A rod extends rearwardly from the plug, along the length of the casing and extensions, and pressure is applied to this rod during driving of the casing to maintain the plug in the operative position. A series of rod extensions are added to the rod when required, in a manner similar to the casing extensions.
When the desired depth is reached, the plug is retracted to abut against a stop in the interior of the casing. The casing is then driven to force soil into the sample casing. The device is then withdrawn from the soil to recover the sample.
The main problem with such a device is the need to drive both the casing (or its extensions) and the plug (or its extensions). The driving of the plug extensions can cause vibrations therein which cause the plug to move slightly out of position, contaminating the sample. Driving of the plug also requires that the plug rod extensions be sufficiently rugged to drive the plug, increasing weight and cost.
Another prior art device overcomes this problem by releasably fixing the plug to the front of a soil sample tube with a locking mechanism during driving. When the desired depth has been reached a cable connected to the locking mechanism is pulled to unlock the mechanism. The casing is driven to collect the sample, and the casing is then removed from the soil to retrieve the sample. This arrangement is disadvantageous in that the locking mechanism is located in the front end of the casing. This necessarily requires a larger outer diameter for the soil sampling tube, which results in increased driving forces being needed to insert the casing into the soil.
Another disadvantage with this type apparatus is that a continuous cable must run from the locking mechanism at the soil sample tube to the soil surface. This usually requires the threading of the cable in to the incrementally added sections of the casing.